Wireless communications have become a popular and essential communications medium both nationally and globally. Over the past twenty years, the number of users of Public Land Mobile Networks (PLMN) or cellular telephone networks has grown to over a billion subscribers using networks that provide geographic coverage throughout the world. While these networks primarily provide voice communications, they also enable relatively low rate data communications (e.g., 9.6-140 kbps).
As these wireless networks have become more integrated with land-line data networks such as the Internet, the desire and demand to extend the features available within the land-line Internet to wireless devices has increased dramatically. World Wide Web (WWW) access, games, multimedia messaging including pictures and sound, music, enterprise applications, and streaming video are among the service capabilities desired using wireless data devices. Unfortunately, the limited data rates of the supporting wireless networks have resulted in unacceptably slow performance when using these services or other data applications.
Recently, PLMN providers have launched CDMA2000 Evolution Data Only (EVDO) networks that provide up to 2 Mbps and Third Generation GSM (3GSM) that provide approximately 300 kbps data rates. Also, the IEEE has standardized Wireless Local Area Network (WLAN) technology including the 802.11 b and 802.11 g standards that provide 11 Mbps or 54 Mbps data rates respectively. The IEEE is working on a new standard referred to as the 802.11 n that will provide data rate greater than 100 Mbps. These newer data standards and networks provide significantly higher data throughput in order to meet the increased demand for wireless data that is needed to enable certain data applications and Internet services within wireless devices. Other wireless data networks also exist including satellite, Specialized Mobile Radio (SMR), private/trunked, Cellular Digital Packet Data (CDPD), fixed wide area networks (WAN), metropolitan area networks (MAN), and personal area networks (PAN) using the Bluetooth protocol or Ultra Wideband (UWB) technology.
PLMN networks are generally referred to as cellular networks because they employ a frequency re-use architecture in which wireless access channels are grouped into geographically-located cells and sectors. The size of each cell depends on the output power of the network base station transceiver associated with each cell. Each access channel uses a certain frequency band in one geographic cell that is re-used in another cell, geographically separated from the first cell, by another access channel where the likelihood of interference is minimized. These networks also use a centralized switch or server to enable a wireless device to move from cell to cell while maintaining a persistent data connection. In the United States, cellular and Personal Communications Service (PCS) networks operate in the licensed commercial 824-849 MHz, 869-894 MHz, 901-941 MHz and 1850-1990 MHz. Access data channels, however, are bandwidth limited to 12.5-150 KHz and 25 MHz, depending on the service offered.
WLAN networks employ wireless access points that communicate with multiple wireless devices simultaneously via a set of fixed access channels. Typically, these networks use contention protocols such as Carrier Sense Multiple Access Collision Avoidance (CSMA-CA) to enable multiple users to share the same wireless access channels emanating from a transceiver access point. These WLAN networks are generally referred to as wireless Ethernet networks because the access mechanism is similar to conventional Ethernet networks. While WLAN networks may be centrally controlled, they are often used by individuals as wireless bridge or router connections to a local area network (LAN). WLAN networks may operate in the 900 MHz, 2.4 GHz and 5.5 GHz unlicensed bands. The 802.11b is limited to a data rate of 11 Mbps, while 802.11b and 802.11g are limited to 54 Mbps. The 802.11n, which is under development, is expected to have a data rate of greater than 100 Mbps.
Two high data rate PAN standards under development are 802.15.3a and 802.15.3c. The former has two competing proposals, namely MB-OFDM and DS-UWB, while the latter is based on the 60 GHz technology. MB-OFDM and DS-UWB have maximum data rate of about 480 Mbps and 1 Gbps respectively at a distance of about 3 meters. The 60 GHz technology is expected to have greater data rate and distance.
While these newer wireless data networks provide improved data throughput for users, the desire for even greater throughput is already creating the demand for higher data rate wireless networks that support advanced data application such as high-resolution video conferencing, HDTV connectivity, broadcast video, video-on-demand, online training, distance learning, peer-to-peer collaboration, file transfers, data mining, database applications (e.g., CRM, ERP), and e-mail with attachments. Furthermore, high data rate wireless networks are arguably less costly than cable or copper to install and maintain by an enterprise or user. Concerns regarding reliability, security, quality of service, and coverage of high data rate wireless networks, however, must be addressed.